The Bernardelli B4 series of gas-operated, tactical combat shotguns was a semi-automatic system utilizing 12-gauge ammunition and designed exclusively for operations by military and security forces. The B4 came about as an answer to the United States JSSAP (Joint Service Small Arms Program) specification calling for a new type of semi-automatic shotgun. The 1970's-era program sought to coordinate weapon standardization between the main branches of the US military.

The resulting B4 proved of high quality and durability and was distinct from other combat shotguns in that it operated from a detachable box magazine instead of a tubular magazine. Additionally, the B4 could be operated as a self-loading weapon or manually using the pump slide. The semi-automatic action was to provide a higher "second hit" probability by not having the operator pump the slide to introduce the follow-up round, thus potentially losing track of his target (if only for a second or two). The shotgun also featured an integrated carrying handle, folding stock and a high-quality steel barrel with an overall anti-glare finish. Ammunition types were all conventional and the weapon could fire from a 3-, 5- or 8-round curved detachable box magazine.

The series, along with its semi-automatic action, were banned from import in the United States, along with several other potential box-fed shotgun systems on the civilian market (including the Italian Beretta M3P and French SPAS-15) - courtesy of the Assault Weapons Ban Act beginning in 1994. The B4 also appeared in a pump-action only model designated as the B4/B. The B4/B visually retained the stock and body of the B4 with some slight alterations to the pump slide and forward section.